1. Field of the Invention
The present invention relates to DSV control apparatus and DSV control method that controls a digital sum value (DSV) to minimize DC (Direct Current) component of input data to generate the data appropriate for transmission or recording to a recording medium.
2. Description of Related Art
When data is recorded to a recording medium such as a magnetic disc, an optical disc, or a magnetic optical disc, it is modulated in appropriate form for the recording. The data is encoded by a modulation method corresponding to their specifications.
When the code created by the modulation is recorded on an optical disc or a magnetic optical disc, Non Return to Zero Inverted (NRZI) encoding is performed. With the NRZI modulation for generating a recording code, a logic 1 is encoded as inverted, and a logic 0 is encoded as non-inverted. The recording to a recording medium such as a disc is performed based on the NRZI recording code.
In the recording to a recording medium, the encoding modulation appropriate for each medium is performed. If DC component is contained in the modulation code, it causes variation in error signals and jitter to occur. The DC component is thus preferably minimized.
To meet this need, the control of a digital sum value (DSV) is performed. DSV is defined as a sum of values when the value of +1 is assigned to the “1” states and the value of −1 is assigned to the “0” states respectively in a code sequence. DSV gives an indication of DC component in the code sequence. Minimizing the absolute value of DSV by performing DSV control suppresses the DC component of the code sequence.
The technique of performing DSV control by inserting DSV control bits when creating a recording code is disclosed for example in Japanese Unexamined Patent Publications Nos. 11-346154, 2003-179497, and so on.
The present invention, however, has recognized that the DSV control method disclosed in therein have a problem that, for some patterns of encoded data, insertion of DSV control bits for DSV control does not lead to a decrease in the absolute value of a sum of values of a code sequence but only diverges the value.